Researcher David Genevier has done some very interesting work by comparing plans from two ancient structures, from different places, traditions and almost a thousand years apart: the Great Mosque of Kairouan in Tunisia, and the earliest plan of the ancient synagogue of Dura-Europos, Syria. His findings have very intriguing cultural, and metrological implications.

Dura-Europos

Dura-Europos was a city built on the banks of the Euphrates river, in 300 B.C. In the mid third century A.D., the city was besieged, captured, and finally abandoned. All of its citizens were deported and the city became a home to birds and animals. Until the recent Syrian civil war, when it was unhappily destroyed, the site was of great archaeological importance. It contained, among other treasures, the remains of an ancient synagogue, uncovered in 1932. There was a forecourt, a house of assembly, many wall paintings, and a Torah shrine in the western wall facing Jerusalem. The last phase of its construction was dated to 244 A.D.

Kairouan

The Great Mosque of Kairouan, or Uqba as it is also known, is a huge, magnificent structure in Tunisia. It was built when the city was founded in 50 A.H., or 670 A.D., by the Arab general and conqueror Uqba ibn Nafiand, under orders from the Caliph Mu'awiya I, in Damascus.

Kairouan was essentially a military outpost in a far corner of the huge empire that was the Ummayad Caliphate. These were dangerous times, and the city was often under attack. Yet it was also important as a religious centre, and served as a base from which not only to maintain military power, but also to convert Berbers to Islam. The mosque at Kairouan would have been very important. Caliph Mu'awiya I may also have built a mosque on Temple Mount, in Jerusalem, according to medieval sources. He must have been involved in the planning of the new mosque in Kairouan.

Kairouan is one of the oldest places of worship in the Islamic world, and is still regarded as the fourth holiest site in Islam. For a long time it was a centre of Islamic thought and science, until the decline of the city in the 11th century. The first structure only stood for around twenty years as it was destroyed by Christian Berber forces. Kairouan was part of a huge empire that stretched from central Asia to Spain, ruled by the Umayyad dynasty in Damascus. After the Abassid takeover, in 760, it was to Spain, in fact, that sole survivor of the mass murder of the Umeyya family, feeling across north Africa, and finally settling in Córdoba. There, Amir Abd El-Rahman set it up his own caliphate, in opposition to the Abbassids. The story of his escape is wonderfully told in a novel by Anthony Fon Eisen.

Just a few years before the disastrous end of the Omeyyad rule, in around 724, orders arrived in Kairouan from the Caliph in Damascus, Hisham ibn Abd al-Malik to further develop the new city. So the mosque that was there, the very first one, was knocked down and rebuilt, except for the mihrab. It is this very first imprint from the archaeological excavations that David Genevier has compared to the plan of the ancient synagogue in Duros-Europa.

The outline in black represents the ground plan of the Mosque in Kairouan, and the outline in orange is the Synagogue in Dura-Europos. As you can see, the two plans seem to match very well in their shape and proportions, though the sizes are different. This suggests the possibility of a common template. Furthermore the ratio between the two different structures in terms of size is 14/3. This would suggest a link in terms of either the units of measure used, or the number of units used, in units of measure related to each other by such a ratio. David has suggested that the architect of the Mosque used plans from the synagogue at Dura-Europos, which would have been in Roman feet, and adapted the measures to Arab units. The dimensions of the Mosque in 670 would have been 103.68 m x 76.80m, or 27 qasab x 20 qasab. the length of the synagogue was 22.22 m, or 75 Roman feet. David argues that in and of itself this provides a potential theoretical link between the Roman and Arab units of measure, and by extension, with the Egyptian and Mesapotamian units also.

Metrology

27 qasab = 200 Nippur cubits = 324 Arab feet = 198 Egyptian royal cubits = 336 Greek feet = 350 Roman feet = 36000 Sumerian grains.

David gives 0.32 metres for the Arab foot, which he relates to the base side of the Great Pyramid, there being 720 Arab feet in it, or 60 qasab.

1 qasab is 3.8400 metres, or 12 Arab feet.

The qasab is an ancient Arabian measurement of length and volume, which translates as "cane".

1 Nippur cubit = 0.5184 m

1 Roman foot = 0.2962 m.

1 Roman foot = 4/7 Nippur cubit, and 1 Roman foot = 4/7 x 99/100 Roman cubits = 99/175 Roman cubits

In particular, David has called into question the 25/27 ratio between Arab foot and Roman foot. Rather, the Roman foot should be seen as 27/25 x 6/7 Arab feet.

With 11.66666 inches for the Roman foot, multiplying it by 6/7 gives 10 inches, and 27/25 gives 10.8 inches. This is the "U" unit, descibed by Flinders Petrie in his 1911 article.

Or starting with a 11.664 inch Roman foot, the same works with an additional multiplication by 4375/4374.

This last ratio is the one that unites the two versions of Berriman's value "k", which is either 1.296 or 1.296296296. It also unites two common values for the digit: 0.729 and 0.729166667 inches.

As David Kenworthy has said:

"It comes from the 3 versions of the meter all 54 digits as 4374 4375 4400 39.366 39.375 39.6"

As David Genevier points out, 4375/4374 = 25^2/27^2 x7/6 , so this ratio is central to the conversion between Arab and Roman feet.

David Genevier points out that the Nippur cubit x 99/100 gives the Egyptian royal cubit. This works with 0.5184 m and 0.513216 m, or with 20.412" and 20.6181818".

To go back to the dimensions of the two structures, at Kairouan and at Dura-Europos, the length of 27 qasab or 103.68m is 5600 fingers of 0.0185m, ie the digit of 0.729 English inches. And we find the number 27 in the relationship between the two sides of the rectangle, since 103.68 x 20/27 = 76.80.

1 qasab q, if it measures 103.68/27 = 3.84 m, is also this digit, but of 0.0185185185 m, not 0.0185 m, multiplied by 12^4 / 100. This digit of 0.0185185185 m is a measurement found by Hero, according to Letronne. This digit is simply a fraction of a 40,000,000 m circumference (40,000,000 / 2 160 000 000 = 0.0185185185), and multiplied by four gives a palm, by twelve a spithame, and by sixteen a foot.

3.84 m are also, if Hero's digit is worth 0.0185185185 m, 2.88 orgyes, 1.08 acenes, or 0.0216 stades. And the 76.8 m are, among other things, 28.8 x 2 orgyes. 76.8 meters are also 146.66666 Egyptian cubits of 20.6181818 inches. And this cubit, multiplied by 146.6666, divided by 2 gives the qasab of 3.84 m. It is clear that all these measures are related to each other. And the 3.84 m is 5.6 times an intriguing measurement of 27 English inches (with 39.375 inches to the metre).

There are links with the English system too 3.84 m are 12.6 English feet, or 4.2 yards. The English yard is 36 inches, or 14.4 x 24 x 0.72916667 / 7 inches = 12 x 12 x 12 x 2 x 0.729166667 / 70 inches, and the English foot = 115.2 / 7 x 0.729166667 inches . So it looks like this yard is the seventh of something. These 3.84 meters are 0.6 x 7 = 4.2 yards.

The width of 20 qasab or 76.8 m divided by 6.4 = 12.

The length of 27 qasab or 103.68 m divided by 6.4 is 16.2.

Mauss's Assyrian and Persian royal foot of 0.658285 m lends itself well to 3.84 meters too, because 35/6 of those feet is 3.84 m. And then there are plenty of others, 3.84 m is 0.7 "U", 7 worker cubits, 6.666 "coudées de l'arroseur", 7.1111 iron cubits / black cubits / cloth cubits, 6 hashemic cubits.

The Nippur cubit of 0.5184 m or 20.412 inches is indeed related to the Egyptian Royal Cubit of 20.6181818 inches or 0.5236363636 m, by a ratio of 99/100.

Royal Assyrian cubit x 175/220 = Royal Egyptian cubit

25.92 x 175/220 = 20.618181818 (inches)

25.92 x 7/22 x 4 = MY inches 32.989 (2.74909 feet)

25.92 x 7/22 x 10/4 = 20.6181818 ERC

25.92 x 700/2 = 9072

GP base perimeter is 14000 Royal Assyrian Cubits, if you accept 9072 inches, or 230.4 metres, per base side,a little bigger than Flinders Petrie's estimate of 9068.8 inches. With pi as 22/7, the height in Royal Assyrian cubits is 4900/22 = 222.72727.

1 Nippur cubit x 400/99 x 22/7 = 1 Royal Assyrian cubit.

The width of the mosque at Kairouan is 76.80 m. In Seville varas of 0.864 metres, this would be 100 x 8/9.

Units of measure from the Middle East were used in Western Europe, in places like France and Spain, and in fact were accepted as standards. This was the case, for example, when Charlemagne, Emperor of the Franks, accepted as the basis for his system an Arab unit.

In Outlines of the evolution of weights and measures and the metric system, (1857) William Hallock writes:

(There follows a note: " The name "esterlin" was employed at one time in the French language to signify "true," being equivalent to the modern Fr. word "veritable." It has, however, disappeared from use, but has been retained in English, with the same signification, in the form of "sterling," as, for example, "pounds sterling."")

So it is curious, that although Charlemagne's grandfather Charles Martel won a decisive victory against an Umayyad invasion of Aquitaine, Charlemagne himself accepted a Middle Eastern standard as a basis for a French system of measure from the successors of the Umeyya, the Abassids. This standard was given the name "esterlin" to denote it's authenticity.

Sunrise and Sunset Star

Another thing of interest is the Great Mosque of Kairouan has a sunrise azimuth of 59.99° and a sunset azimuth of 300.01° at the summer solstice. See here.

So it would be as if the sun rose in the tip of a great hexagon, or six pointed star, across the land, and then set in another. In fact the sun dial at the mosque is in the shape of a hexagon.

Maybe the reason for the shape is the summer solstice pattern of the sun.

Elsewhere on this latitude, Tehran's Golestan Palace also fits this pattern.

I looked up the summer solstice sunrise info for Córdoba - because that's where the last prince of the Umeyya settled. There was another six-pointed star, although not quite as precise. You would want a near perfect 60 degrees for the sun rise azimuth, but it's 58.98. I checked the historical values for the earth's obliquity and this summer solstice star would have been just about perfect in the past; obliquity today is 23.44 degrees, decreasing at a rate of 0.013° per century, I believe, and the angle of obliquity required would be 23.53°, so about 31 centuries ago a 60 degree sunrise at Córdoba would have worked perfectly.) Perhaps Kairouan was seen as an updated marker for a place where the sun rose and set in the points of a six-pointed star at the summer solstice, after Córdoba.

So there are many fascinating things to discuss as a result of David Genevier's findings, both historical and metrological.

Photos

David Genevier visited Kairouan recently and he was kind enough to share some of his photos of the mosque. There really convey a sense of the space, and of peace. They are also very interesting in that you can guess the contours of the first mosque, and David's diagrams present these clearly. There are several photos of the immense courtyard, and of the beautiful sun dial. The first photo below is of the dig, and the diagram below shows the limit of the first mosque with a green arrow. See below. Then the two are put together to illustrate this. Thank you David!

Bibliography

Hallock, William, 1857, Outlines of the evolution of weights and measures and the metric system, the Macmillan company, New York

Mauss, C, 1892, “L’ÉGLISE DE SAINT-JÉRÉMIE A ABOU-GOSCH OBSERVATIONS SUR PLUSIEURS MESURES DE L’ANTIQUITÉ (Suite).” Revue Archéologique, vol. 20, 1892, pp. 232–53. JSTOR, http://www.jstor.org/stable/41747039. Accessed 6 June 2023.

Letronne, Jean-Antoine, 1851, Recherches critiques, historiques et géographiques sur les fragments d'Héron d'Alexandrie our du systeme métrique égyptien, Imprimerie Nationale, Paris